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<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Get approximate polar equation for given image</title>
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="description" content="">
  <meta name="author" content="">
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  <script>
    var img, url;

    window.onload = function() {
      // DOM File object selected
      var file = document.getElementById('file').files[0];

      if (file) run();
    }

    function run() {
      // DOM File object selected
      var file = document.getElementById('file').files[0];

      url = window.URL.createObjectURL(file);
      img = new Image();
      img.src = url;

      img.onload = readPixels;
    }

    function readPixels() {
      window.URL.revokeObjectURL(url);

      var canvas = document.createElement('canvas');
      canvas.width = img.width;
      canvas.height = img.height;

      document.body.appendChild(canvas);

      var ctx = canvas.getContext('2d');
      ctx.drawImage(img, 0, 0, img.width, img.height);

      var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);

      var mask = new Uint8Array(imageData.data.length / 4);
      var width = canvas.width;
      var height = canvas.height;

      var o = [(img.width / 2) | 0, (img.height / 2) | 0];
      var d = window.d = [];

      // paint red on the center pixel (not really visible)
      imageData.data[(o[1] * width + o[0]) * 4] = 254;

      for (var theta = 0; theta < 2 * Math.PI; theta += 0.01) {
        var dx = 1 * Math.cos(theta);
        var dy = - 1 * Math.sin(theta);
        var i = 0;

        var x = o[0];
        var y = o[1];
        var intX = x;
        var intY = y;
        while (true) {
          x += dx;
          y += dy;

          intX = x | 0;
          intY = y | 0;

          if (intY < 0 || intY > canvas.height || intX < 0 || intX > width) {
            break;
          }

          var ptr = (intY * width + intX) * 4;
          var tone = imageData.data[ptr] +
            imageData.data[ptr + 1] +
            imageData.data[ptr + 2];
          var alpha = imageData.data[ptr + 3];

          // draw a green line all the way until the boundary
          imageData.data[ptr] = 0; // R
          imageData.data[ptr + 1] = 254; // G
          imageData.data[ptr + 2] = 0;  // B
          imageData.data[ptr + 3] = 254;

          // are we there at the boundary?
          if (alpha < 128 || tone > 128 * 3) {
            d.push(i);
            break;
          } else {
            i++;
          }
        }
      }

      ctx.putImageData(imageData, 0, 0);

      var max = d.reduce(function(prev, curr) {
        return Math.max(prev, curr);
      });

      var resultText =
        'function(theta) {\n' +
        '  var max = ' + max + ';\n' +
        '  var leng = ' + JSON.stringify(d) + ';\n\n' +
        '  return leng[(theta / (2 * Math.PI)) * leng.length | 0] / max;\n' +
        '}\n';

      var result = document.getElementById('result');
      result.textContent = resultText;
    }
  </script>
</head>
<body>
  <div class="container">
    <p class="lead">Get approximate polar equation for given image.</p>
    <p>
      Please select a black-white image below.
      The black part shall be centered and it will be the shape to trace.
      You would have to manually save, edit the code if you want any additional processing.
    </p>
    <form>
      <input type="file" id="file" class="input-large" onchange="run()">
    </form>
    <pre id="result"></pre>
  </div>
</body>
